Casualty’s Dr Zoe Hanna spends her time saving lives and having disastrous flings with men, all the while groomed to within an inch of her life in designer frocks and high heels.

But for this week’s explosive two-part finale to the 29th series, Sunetra Sarker, who plays her, found herself looking less than impeccable. Instead, she had to be soaking wet for almost five weeks while filming Zoe’s climactic scenes, which occur during her wedding to hospital porter Max Walker (Jamie Davis).

“Who would want to play drowning in TV land?” asks Sunetra, 42, laughing, when we catch up to discuss Zoe’s cliff-hanging storyline. “It involves night shoots from 5pm until 5am and me being constantly hosed down by a fire crew to make sure I was dripping wet for every scene.

“I was freezing and looked like a drowned rat. I’m not the best swimmer in the world, either, but I did what I could and we cheated it for the cameras. The entire story was a real adventure for me.”

The breathtaking scenes, filmed in Pinewood Studios’ water tank, come at the end of Zoe and Max’s wedding day. “A fire starts and spreads during the wedding party and everyone gets dispersed,” adds Sunetra. “Then there’s an explosion and Zoe, who’s snuck off on her own to have a moment, ends up in the water.”

In other words, it ends almost as badly as it starts. The truth is that despite an ardent following among Casualty fans, Zoe and Max’s relationship never looked good on paper. She’s a successful, driven, forty-something career woman with commitment issues, he’s a laid-back hospital porter a decade her junior. She can’t have children, and Max’s mother doesn’t like her.

Nothing can ever be the same again

Yet in spite of these obvious impediments the two were swept away on a tide of emotion – Max rashly popped the question and Zoe accepted.

And as the nuptials draw near, Zoe is having doubts. “Zoe’s commitment-phobic and selfish. Having a husband was never on her to-do list,” Sunetra says.

And there’s another reason this wedding may prove disastrous – Zoe is hiding something. “Something happens between the two episodes, when Zoe stumbles and has a decision to make, and she wakes up on her wedding day with that still to be made,” explains Sunetra. “She’s got a secret and the secret isn’t revealed until the last episode. It’s a life-changing one – nothing can ever be the same again. Max doesn’t know it.”

Oh dear, the chances of that happy-ever-after that ‘Zax’ fans have been longing for is ebbing fast. But Sunetra is delighted Casualty devotees have taken the couple to their hearts. “Fans have gone crazy for Max and Zoe” she says. “Older women stop me to say, ‘Go for it – why can’t you have a toy boy?’, while younger girls say it’s the sweetest romance ever.”

Whether they get to enjoy married life is a question that will extend into the start of series 30, which begins the following week. Zoe, still dripping wet, features heavily. And although there’s high drama for the wedding party, the atmosphere on set has been light.

Sunetra has a sunny personality, and it’s no wonder as her happy personal life is in stark contrast to Zoe’s. Divorced amicably from Nick Corfield, with whom she has a son, 10-year-old Noah, Sunetra has been loved up with boyfriend Scott Carey, a marketing director, for three years. “He has two children around the same age as Noah, and we’re a very modern family,” she smiles. “Scott and I are very together and we’re solid.”

Last year, she made a splash on Strictly Come Dancing, finishing sixth, and in December she will have been in Casualty for eight years. “I can’t say it’ll go on forever but for now I’m definitely here until the end of 2015,” says Sunetra.

And she’s revelling in the spotlight for the next few episodes as Zoe, whose future is looking uncertain. “I’m really enjoying playing Zoe in a non-medical context for once,” explains Sunetra. “You do see a wedding and it is a success in many ways, but, in true Casualty form, the wall comes tumbling down.”